Low velocity gas burner



- "in. ad I Dec. 20, 1960 Filed Dec. 2, 1958 D. A. CAMPBELL LOW VELOCITYGAS BURNER 2 Sheets-Sheet 1 INvaN-roa DONALD A.CAMPBELL Dec. 20, 1960 D.A. CAMPBELL LOW VELOCITY GAS BURNER 2 Sheets-Sheet 2 Filed Dec. 2, 1958INvEN'roR DONALD A.CAMPBELL L'OW VELOCITY GAS BURNER Donald A. Campbell,Rockford, Ill., assignor to llclipse Fuel Engineering (30., Rockford,111., a corporation of Illinois Filed Dec. 2, 1958, Ser. No. 777,704

8 Claims. (Cl. 158-113) The present invention relates to gas burners andhas particular reference to a gas burner of novel design capable ofproducing a low velocity flame of wide expanse wherein the flame isdeveloped within a comparatively short combustion zone.

There are many industrial applications in which it is desirable todevelop a large expanse of radiant surface which may be directed towardan item to be heated and from which surface the flow of combustion gasesare at a low velocity. For example, in glass annealing furnaces it isnecessary to uniformly heat a large area of glass with no localizedheating or hot spots resulting from flame impingement. The burnerrequirements for such furnaces therefore are the production of a flameof large expanse which may be directed against the work in closeproximity thereto, uniformity of flame temperature throughout the entireflame area, minimum turbulence within the flame structure, and lowforward velocity of the products of combustion. Large flame expanse isobviously necessary in a single burner furnace. Uniformity oftemperatuer must be maintained to prevent localized heating of the work.Minimum turbulence is desirable since any form of flame turbulence, onceinitiated within a flame structure cannot be controlled and the presenceof turbulence is apt to creat uncontrollable eddy currents and localizedheating by convection. Low forward velocity is a requirement forsubstantially the same reason and for the additional reason that with ahigh forward velocity flame length is increased at the expense ofaccurate heat control in the vicinity of the work.

Burners constructed in conformity with the above requirements may findwide industrial application other than for the annealing of glass, asfor example in the heating of galvanizing kettles, for firing meltingfurnaces, flat roof rotary heat treatment furnaces, billet heaters,cover fired ladles, process tubing heaters and a wide variety of otherinstallations too numerous to mention. For an all purpose low velocity,flat flame combustion type burner of the type set forth above, verticalfiring in either direction, horizontal firing, or firing at anyinbetween angle is a further consideration that must be borne in mind.

The above industrial requirements for large area surface heating arereadily and conveniently met by the use of radiant electric heaters and,where electric power is available at moderate cost, many such heatersare employed. The use of electrically generated radiant heat naturallysuggests the use of radiant heat in connection with combustion heatingfor the same purpose, since the uniformity of heat which is generated byradiant energy is too well known to need discussion. By constructing acombustion burner which depends to a large extent upon the generation ofradiant heat by a radiant element after absorption of heat by thatelement from combustion gases by a process of convection, the workundergoing treatment may be spared the consequences of contates Patentice vection heating, for example localized heating and poor heat controland, in some instances, undue oxidation.

There are on the market and in current use burners which meet the aboveoutlined large area, low velocity flame requirements and whichfurthermore depend for their efficiency upon a large measure of radiantheat being generated. Many of these burners consist of concaverefractory shapes of cup-shape configuration through which premixed gasand air is deliveerd for combustion purposes and then deflected alongthe inside walls of the refractory cup. Such burners require some methodof premixing the gas and air, as for example the use of a fuelproportioning apparatus, and they are subject to fre quent backfiring.

The present invention is designed to overcome the above-notedlimitations that are attendant upon the use of such burners which usepremixed gaseous constitutents for combustion purposes and, toward thisend, briefly, it contemplates the provision of a burner assembly including a relatively simple burner casting of novel design capable ofdeveloping a highly radiant surface by means of gas combustion andincorporating the advantages of a nozzle burner in that it has a widerrange of heating capacity, is not subject to backfiring, and isextremely simple to control. The provision of a burner construction ofthis type is an important object of the present invention and, incarrying out this object, the invention contemplates the provision of aburner casting having separate gas and air passages and arranged todeliver the gas and air at the outside circumference of a generallycircular refractory or other radiant eement. Small streams or jets ofthe gas and air are delivered to each of a series of circumferentiallyarranged spaced localized combustion regions and provision is made forcausing the gas and air to interrnix at or near the periphery of theradiant element with the products of combustion sweeping across thefront face of the radiant element so that the latter will absorb heattherefrom for subsequent radiation forwardly against the work. Mixingand com bustion takes place at or close to the surface of the refractoryor other radiant element and provision is made whereby the combustiongases, during and after combustion, assume a circular motion which isconducive toward intimate mixing and substantially complete dissipationof heat with an extremely small component of forward motion. Stated inother words, the necessary turbulence for intimate mixing of the gas andair and consequent complete combustion is directed in a circular pathrather than in an axial path so that an extremely short flamecharacteristic is attained.

For a better understanding of the invention, its advantages, andspecific objects attained with its use, reference may be had to theaccompanying two sheets of drawings and the following descriptive matterwherein a preferred embodiment of the present burner has been shown anddescribed.

in these drawings:

Fig. l is a front elevational view of a burner assembly constructed inaccordance with the principles of the present invention;

Fig. 2 is a sectional view taken substantially along the line 2-2. ofFig. l and schematically illustrating certain flame and radiant heatcharacteristics which are associated with the use of the present burner;and

Fig. 3 is a fragmentary rear elevationalview of a limited portion orsector of the burner assembly. 7 7

Referring now to the drawings in detail, the burner assembly of the formof the invention selected for illustration herein involves in itsgeneral organization a main burner casting N9 of generally cylindricaldesign and or dished or cup-shaped external configuration. The can: ingis provided with a flat circular rear wall'1'2,'a'stepped,

dished cup-shaped front wall 14 and an interconnecting generallycylindrical outer wall 16 having a special shapecharacteristic whichwill be described presently. The three walls 12, 14 and 16 define aninternal space or chamber which is divided into an air chamber 18 and agas chamber 20 by means of a cup-shaped intermediate partition wall 22,the circular rim of which is joined to the front wall 16. A circular webor boss 24 connects the rear and intermediate walls 22 at the centralregions thereof and communicates with a threaded inlet opening 24designed for threaded reception therein of one end of a gas supply pipe26 whereby gas may be admitted to the interior of the chamber 20. Therear wall 12 is formed with an opening 28 in the peripheral regionsthereof having a thickened boss portion 30 which may be tapped as at 32(Fig. 2) for reception of the clamping screws 34 by means of which abolting flange 36 associated with a suitable pipe fitting 38 may besecured in position over the opening 28. The fitting 38 is designed forconnection to a suitable air supply pipe (not shown) whereby air may beintroduced into the interior of the chamber 18.

The front wall 14 is of circular stepped, dished configuration andincludes an extreme forward annular Wall section 40, an intermediateannular wall section 42, and a rear inside or bottom section 44. Acylindrical wall section 46 connects the sections 40 and 42, while asimilar cylindrical wall section 48 connects the wall sections 42 and44. The steps of the front wall 12 thus provide a shallow circulardepression, of which the wall portion 42 and the wall portion 44constitute the bottom wall.

The cylindrical outer wall 16 is formed with a radial flange 50intermediate its ends. The flange 50 has secured thereto by means ofbolts 52 a ring member 54 by means of which the burner as a whole may beoperatively secured to a furnace wall, such as the wall shown at 56 withthe burner projecting through a furnace opening 58 provided in the wall,clamping bolt 60 being employed for securing purposes.

Suitably secured, as 'by cementing, within the dished, cup-shaped frontwall 14 of the burner casting is a radiant element 62. This element may,according to the present invention be formed of various materialscapable of heat absorption and radiation, as for example a refractory orceramic material, asbestos block, metal alloy, etc. In the illustratedform of the invention the element 62 is formed of a refractory materialand is generally of mushroom configuration and is formed with a shortstem portion 64 and a crown portion 66 preferably, but not necessarily,presenting a convex forward or outer face 68. The stem portion 64 of theradiant element 62 seats within the bottom region of the front wall 14and the rim region of the crown portion 66 seats on the annular wall 42.The crown apex may project a slight distance forwardly of the plane ofthe forward annular wall or face 40 of the burner casting. The crownportion 66 of the radiant element 62 is provided with a shortcylindrical outer face 70 which is spaced inwardly a slight distancefrom the cylindrical wall section 46, thus defining an annular pocket 72in the forward face of the burner structure, considered as a whole. Thepocket immediately surrounds the convex face 68 of the element 62.

Extending around the forward end of the burner casting is a refractoryor radiant ring or combustion block 80 which may be formed of the samematerial as that of the element 62, and which seats within the spaceexisting between the cylindrical wall 16 and a forwardly extendingcircular flange 82 provided on the ring member 54. The radiant orrefractory ring overhangs the front annular wall 40 of the burnercasting 10 and is formed with a forwardly and outwardly flaredfrusto-conical surface 84, the slant angle of which may be in theneighborhood of 45? although the specific angle selected is notcritical,

and the slant height of which is relatively short. The

the longitudinal axis of the burner casting it). The small base of thecone frustum defining the surface 84 lies close to the outer burner rim,i.e. the circular juncture between the wall sections 40 and 46, whilethe large base of the cone frustum is of a diameter slightly greaterthan the overall diameter of the burner casting 10.

The annular pocket or recess 72 communicates with the gas chamber 20 bymeans of a series of small gas passages 92 which extend through the wallsection 42 at the bottom of the pocket. A similar series of small airpassages 90 extend through the wall section 46 near the forward rimthereof and establish communication be tween the pocket 72 and the airchamber 18. The passages 90 and 92 are arranged in pairs, which is tosay that each port 90 in the wall section 46 is in close proximity to aport 92 in the wall section 42 with the port locations being aligned inthe same radial plane. The ports 92 extend in a longitudinal directionwhile the ports 90 converge or are inclined forwardly and inwardly at anangle of approximately 85" with respect to the longitudinal axis of thecasing. This angle is not critical and it is selected preferably so thatthe stream or jet of air issuing therefrom within the combustion ring orblock 80 will be directed tangentially inwardly across the peripheralregions of the convex surface 68 of the refractory element 62. The pairsof passages and 92 are circumferentially and equally spaced around theperiphery of the element 62 and, while in the illustrated embodiment ofthe invention twenty-four such pairs of passages have been illustrated,it will be understood that a lesser or greater humber thereof may besupplied if desired. Generally speaking, the diameter of the burner willcontrol the number of pairs of passages employed.

As best illustrated in Fig. l, the air passages 90 do not extend intruly radial planes. In addition to their slight forward inclination, aspreviously described, these passages have their axes extending alonglines which are tangent to a small circle which is concentric with theburner axis as indicated by the dotted lines a, a, etc. and the dottedcircle b.

In the operation of the burner assembly, the pressure of air maintainedwithin the chamber 18 is usually appreciably greater than the pressureof gas within the chamber 20. As a consequence, small jets or streams ofgas will issue from the various passages 92 and be picked up so tospeak, by the more forceful jets of air issuing from the passages 90 andadmixture and combustion will take place as the two comingling streamsmove inwardly across the convex face 68 of the radiant element 62. Atthe central region of the convex face 68 there will be impingementbetween the comingling streams issuing from all of the various pairs ofpassages 90 and 92 and, due to the tangential impact which takes placeat this region, a swirling or circular motion will be set up. Due to thedistance between the central axis of the burner casting, and also due togas expansion upon combustion thereof, the impacting streams at thecentral region of the burner structure will have considerably largervolume than the combined volume of the streams as they emerge from thepassages 90 and 92. As a con' sequence, considerable turbulence will be.set up within the combustion block or ring 80 but this turbulence willbe of a controlled nature in that its resultant vectorial component ofmotion will be in various tangential directions extending around theburner rather than in axial direction. In other words, the rotary motionwhich is developed within the combustion ring 80 will appreciably dampenor restrict the forward velocity of the products of combustion so thatan extremely short flame will result.

During such travel of the products of combustion as described above,much heat will be generated at or near the front convex face 68 of theradiant element 72. The pressures maintained in the air and gas chambers18 and 20 respectively are preferably such that stoichiometric gasairratios exist Within the combustion block or ring 80, thus leading tosubstantially complete combustion of the gas and air with neither excessair nor excess gas remaining which would exert a cooling effect withinthe combustion space. Thus maximum temperatures will be attained in thisregion. Due to the fact that heat is generated at or near the face ofthe radiant member 62, much of this heat will be absorbed by the memberand subsequently radiated forwardly therefrom. This radiant heat will beof a uniform nature as is characteristic of radiated heat when issuingfrom a surface of large expanse.

The essential and operative elements of the improved burner assembly ofthe present invention have been described above and certain alternativeor auxiliary instrumentalities such as peep-sight, piloting andelectrode devices 160, I02 and N4 respectively (Fig. 3) are believed torequire no detailed description. It is deemed sufficient to state thatprovision is made for these devices by affording a thickened region 106(Fig. 2) in the casting body in the upper region thereof and providingtapped holes therein for removable reception thereof.

While one specific and preferred form of the apparatus by means of whichthe principles of the invention may be carried out has been illustratedand described herein, it will be understood that this form of apparatusdoes not by any means indicate the only form contemplated. The formillustrated herein is only one which has been developed for commercialapplication of the process.

The invention is not to be understood as limited to the detailsdescribed since these may be modified within the scope of the appendedclaims without departing from the spirit and scope of the invention.

Having thus described the invention what I claim as new and desire tosecure by Letters Patent is:

1. In a gas burner assembly of the character described, in combination,a burner casing in the form of a hollow body of generally cylindricaldesign including a front wall, a rear wall and an interconnecting outerwall, a partition wall dividing the interior of the easing into a gaschamber and an air chamber, a supply pipe for gas in communication withsaid gas chamber, a supply pipe for air in communication with said airchamber, said front wall being dished to provide a shallow circulardepression therein which is bounded, at least in part, by a shortcylindrical section of the dished front wall, and a radiant elementnested within said depression and having a peripheral surface spacedinwardly a slight distance from said cylindrical section of the frontwall, said peripheral surface, in combination with said cylindricalsection of the front wall and the bottom wall of the depression,defining an annular trough-like pocket surrounding the radiant element,there being a series of circumferentially spaced small air passagesextending through the cylindrical section of the front wall andestablishing communication between the pocket and the air chamber, saidair passages being disposed substantially in a common transverse planeof the burner casing which is slightly forward of the front peripheraledge of the radiant element, said air passages having their longitudinalaxes extending in directions which are approximately radial, saidlongitudinal axes of the air passages being substantially tangent to acircle of relatively small radius and which is coaxial with the burnercasing and which lies slightly forwardly of the front face of saidradiant element, there being an annular series of spaced small gaspassages in said bottom wall of the depression establishingcommunication between said poeket and the gas chamber.

2. In a gas burner assembly of the character described, the combinationset forth in claim 1 wherein said longi- 5 tudinal axes of the airpassages are inclined forwardly and inwardly of the casing at a slightangle to said radial plane.

3. In a gas burner assembly of the character described, the combinationset forth in claim 1 wherein said radiant element presents a curvedforward surface and wherein said longitudinal axes of the air passagesextend substantially tangential to said curved forward surface.

4. In a gas burner assembly of the character described, the combinationset forth in claim 3 wherein said radiant element presents asubstantially frusto-spherical forward surface.

5. In a gas burner assembly of the character described, the combinationset forth in claim 3 wherein said radiant element presents asubstantially frusto-spherical forward surface of convex configuration.

6. In a gas burner assembly of the character described, in combination,a burner casing in the form of a hollow body of generally cylindricaldesign including a front wall, a rear wall and an interconnecting outerwall, a partition wall dividing the interior of the easing into a gaschamber and an air chamber, a supply pipe for gas in communication withsaid gas chamber, a supply pipe for air in communication with said airchamber, said front wall being dished to provide a shallow circulardepression therein which is bounded, at least in part, by a shortcylindrical section of the dished front wall, and a radiant elementnested within said depression and having a peripheral surface spacedinwardly a slight distance from said cylindrical section of the frontwall, said peripheral surface, in combination with said cylindricalsection of the front wall and the bottom wall of the depression,defining an annular trough-like pocket surrounding the radiant element,there being an annular series of circumferentially spaced small gaspassages extending through the bottom wall of the depression andestablishing communication between the pocket and the gas chamber, therebeing a series of circumferentially spaced small air passages extendingthrough the cylindrical section of the front wall and establishingcommunication between the pocket and the air chamber, said air passagesbeing disposed substantially in a common transverse plane of the burnercasing which is slightly forward of the front peripheral edge of theradiant element, said gas and air passages being arranged in pairs withthe air passage of each pair being disposed in close proximity to andforwardly of the gas passage of said pair and in the same longitudinaltransverse plane, the longitudinal axes of the air passages beingsubstantially tangent to a circle of relatively small radius and whichis coaxial with the burner casing and which lies slightly forwardly ofthe front face of said radiant element.

7. In a gas burner assembly of the character described, the combinationset forth in claim 6 wherein said longitudinal axes of the air passagesare inclined forwardly 81nd inwardly of the casing at a slight angle tosaid radial p ane.

8. In a gas burner assembly of the character described, the combinationset forth in claim 6 wherein said radiant element presents a curvedforward surface and wherein said longitudinal axes of the air passagesextend substantially tangential to said curved forward surface.

References Cited in the file of this patent FOREIGN PATENTS

